Use of oxidized cationic starch in flocculation and dewatering of municipal sludge

ABSTRACT

This disclosure covers the use of a cationic oxidized starch in the flocculation and dewatering of municipal raw primary sludge. From 0.016 to 0.1895% (based on the dry weight of the sludge) of the treated starch of 35 to 60 fluidity and 1.75 to 2.25% oxidation is added to the municipal sludge and contacted with the sewage for a period of 3 to 5 minutes before being dewatered to a moisture content below about 70% moisture, which is the moisture level at which the solids will adequately sustain combustion. The starch has from 0.15 to 0.25 degree substitution of an amine butene halide, specifically, 1-chloro-4-butenyl-trimethylammonium chloride.

United States Patent 11 1 1111 3,875,054

Hunt et al. Apr. 1, 1975 USE OF OXIDIZED CATIONIC STARCH IN 3.157.59411/1964 Nevers 260/233 R FLOCCULATION AND DEWATERING OF 3,397,139 8/1968Sak 1 210/53 3,624,070 11/1971 Hunt 260/233 R MUNICIPAL SLUDGEInventors: Walter G. Hunt, Bridgeton; Ray J.

Belz, Mehlville, both of Mo.

Anheuser-Busch Incorporated, St. Louis, Mo.

Filed: Mar. 4, 1974 Appl. No.: 447,656

Related US. Application Data Division of Ser. No. 335.518, Feb. 26.1973, Pat. No. 3.835.114.

Assignee:

References Cited UNITED STATES PATENTS Primary E.\'anzinerSamih N.Zaharna Assistant Examiner-Peter A. Hruskoci Attorney, Agent, orFirmGravely, Lieder & Woodruff [57] ABSTRACT This disclosure covers theuse of a cationic oxidized starch in the flocculation and dewatering o1-municipal raw primary sludge. From 0016 to 0.189591 (based on the dryweight of the sludge) of the treated starch of 35 to 60 fluidity and1.75 to 2.25% oxidation is added to the municipal sludge and contactedwith the sewage for a period of 3 to 5 minutes before being de-' wateredto a moisture content below about 70% moisture, which is the moisturelevel at which the solids will adequately sustain combustion. The starchhas from 0.15 to 0.25 degree substitution of an amine butene halide,specifically, 1-ch1oro-4-butenyltrimethylammonium chloride.

5 Claims, No Drawings USE OF OXIDIZED CATIONIC STARCH IN FLOCCULATIONAND DEWATERING OF MUNICIPAL SLUDGE This is a division of applicationSer. No. 335,518, filed Feb. 26, 1973, now U.S. Pat. No. 3,835,114v

BACKGROUND OF THE INVENTION Presently treatment of raw sewage is a veryimportant problem in the United States, and particularly to the largercities which discharge part of the sewage treatment product into nearbyrivers. In the treatment of municipal raw primary sewage, the sewagegenerally is initially deposited in a settling basin and the effluent ispumped directly to a river or other depository. The effluent may befurther treated, in a secondary treatment process. The solids or sludgefrom the settling basins are filtered (generally on a rotary drumfilter) and the filter cake is taken directly to an incinerator. Thisfilter cake material usually needs to have about 30% solids so that itwill adequately sustain combustion in the incinerator. This is called aprimary sewage treatment and most cities either have or soon will havesuch processes in operation.

The sludge is negatively charged and an anionic polymer usually is addedto the sludge before the cationic polymer is added. If only a cationicpolymer is added the sludge does not flocculate as well as when theanionic material is used in combination.

The cationic material causes the sludge to fiocculate so that the sludgeis more easily filtered and a greater percentage of water can be removedby the filter. As mentioned, the dewatering apparatus presently used ina rotary vacuum filter. The present state of the art also utilizes limeand ferric chloride as chemical coagulants in the treatment of rawprimary sludge prior to vacuum filtration. Certain acrylic-type polymersalso are useful in the treatment of sludge to condition. it for vacuumfiltration.

There are certain teachings of the use of quaternary ammonium starchethers as flocculants, particularly in the patents of Paschal] U.S. Pat.No. 2,995,513 and Caldwell U.S. Pat. No. 2,975,124. Both of thesepatents relate 'to the use of starch ethers as fiocculants. However,neither of these patents disclose the specific starch ether of thepresent invention (which contains a double bond) or its use as a sludgeflocculant, and it is, therefore, a principal object of this inventionto provide a cationic oxidized starch ether of specific characteristicswhich is useful as a flocculant in the treatment of primary sewagesludge at a reasonable cost. It is also an object of this invention toprovide an oxidized starch product which has both anionic and cationicproperties and which is very useful as a flocculating agent in thetreatment of sewage sludge. These and other objects and advantages willbecome apparent hereinafter.

This invention comprises the use of an oxidized gelatinized cationicstarch as a flocculating agent for primary sewage sludge.

DETAILED DESCRIPTION In Hunt U.S. Pat. No. 3,624,070 (assigned to theowner of the present invention), there is shown the preparation ofgranular gelatinizable quaternary ammonium starch ethers from starch andan amine alkene halide. In the present application an oxidized starch isgelatinized prior to reaction with the amine alkene halide so that amore random type of substitution is obtained. This enhances theflocculating effect of the starch ether. Also, the starch must begelatinized prior to use, and the gelatinization prior to reaction alsohas the advantage of preparing a ready-to-use final product.

As will be described in detail hereinafter, it is important that thestarch be oxidized to a specific range; that it be gelatinized prior toadding amine alkene halide; that the substitution be within a specifiedrange, and that a specific amount of the starch ether be added to thesludge in order for the invention to be effective.

Hunt U.S. Pat. No. 3,624,070 discloses methods of making the aminebutene halide starch ether. However, this patent discloses the reactionwith the starch in granular form. In the present invention, the starchis initially treated with sodium hypochlorite until it is oxidized to anavailable chlorine content of about 2.2%. The starch preferably is dentcorn starch, but can be other non-waxy starches such as wheat, potato,sago and rice. The oxidation treatment preferably is with sodiumhypochlorite but can be any other suitable oxidizing treatment, such assodium periodate.

The dent corn starch is oxidized to an available chlorine content ofabout 1.75 to about 2.25%. This oxidation treatment can be carried on byany suitable method, but should be carried to the extent that it isequivalent to a sodium hypochlorite treated corn starch of thisavailable chlorine content. Preferably, the available chlorine contentis about 2.2%. The fluidity of the oxidized starch is about 35 to about60.

In making up the amine butene halide reagent, we prefer to use thetertiary amines, since under the conditions used, they do not furtherreact with halides to form a variety of products as do the primary andsecondary amines, thereby reducing the yields and purity of the reagent.Of the tertiary amines, trimethylamine appears to offer the mostadvantages, not only because it is the most economical but also becauseof its reactivity in this reaction; however, other teritary amines suchas dimethyl benzyl, dimethyl lauryl (Armeen DM12D), and triethyl arealso very reactive. Higher molecular weight teriary amines such astri-n-propyl, N-methyl morpholine, N-methyl piperidine, methyldiallylamine, and pyridine may also be used, but the alkylation reactionrates are considerably diminished. All tertiary amines capable ofquarternizing with dichlorobutene also fall within the scope of thisinvention. Though the free amines are preferred, the corresponding aminesalts may also be used after adding sufficient alkali to revert them tothe free amines.

PROCESS FOR SODIUM HYPOCHLORITE TREATING CORN STARCH In reacting sodiumhypochlorite with dent corn starch, from about 2.0 to 2.25% by weight(based on the dry weight of the starch) available chlorine is reacted atto F. with about 42 to 50% by weight starch (dry basis) based on thecombined water and starch which has been adjusted to pH 9.0 with a 2.0%

NaOH solution. The sodium hypochlorite is added then adjusted to pH 6.5to 5.0 with lzlHcl and diluted with excess water to 15Be, filtered onBuchner funnel. reslurried to 15Be, filtered again and dried.

The amine butene halide reagent described in Hunt US. Pat. No. 3,624,070is the same reagent that is used in this invention. This reagent isknown as amine alkene halide salt and this term is understood to includequa ternary ammonium alkene halide salts. The reagent is represented bythe following structural formula:

R X-G-IL RX Where X is halide, R is methyl or ethyl and G is alkenylene.The alkenylene has from 1 to 4 carbons.

This product is reacted with gelatinized oxidized dent starch to producethe following product:

if Starch-O-G-N RC1 Where R is methyl or ethyl and G is alkenylene of 1to 4 carbons.

One main difference between the starch reaction product of Patent No.3,624,070 and the starch reaction product of this invention is thegreater amount of amine butene halide added to the starch of the presentreaction. Also, the starch is reacted in gelatinized condition ratherthan being reacted in granular form.

In reacting the amine butene halide (particularly 1-chloro-4-butenyltrimethylammonium chloride) with starch, from about 50m55% by weight (based on the dry weight of the starch) of the aminealkene halide is reacted with oxidized gelatinized starch for 4 to 5hours at a temperature of about 65 to 75C. using the technique of Ex.No. 1. The final product has a carboxyl number of about 0.1% to about0.3% which corresponds to a degree of substitution (D.S.) of about0.0036 to about 0.0108. The average molecular weight is about 89000.

EXAMPLE NO. 1

' ring. Specifically, the starch is treated with steam at a temperatureof 212 to 220F. for a period of 5 to minutes while being stirred.

The temperature is adjusted to 70C. and the stirring is continued. Atthis point 32 g. of a NaOH solution is added to the mixture ofgelatinized starch and water with continued stirring. The NaOH is addedas a catalyst and not as a gelatinizing agent. From about 12 to about18% by weight NaOH (based on the dry weight of the starch) can be added.The temperature can be to 75C.

At this point, 1 l l g. of a 50% TAC solution 1-chloro-4-butenyltrimethylammonium chloride) is added. This reagent isprepared as hereinbefore described. This solution is allowed to reactfor 4 hours with stirring at C. before it is diluted to 25% solids byweight with water to product a gelatinized oxidized cationic starch.

From about 50 to about 55% by weight (based on the dry weight of starch)of the amine butene halide can be used. This reaction between the aminebutene halide and the starch can continue for 4 to 5 hours at atemperature of 65 to C.

Following are Examples of treating raw primary sewage with the cationicoxidized starch of this invention.

EXAMPLE NO. 2

A mixture of 108 g. (dry basis) 7303 (lightly oxidized dent starch) in300 ml. water is gelatinized with steam and diluted with 300 ml. water.The dent starch had a chlorine content of 2.20 The gelatinized starch istransferred to a 70C. water bath and 32 g. of 50% NaOH solution and 11 1g. 50% TAC solution are added. The TAC is1-ch1oro-4-butenyltrimethylammonium chloride. This mixture is reactedfor 4 hours at 70C. The resultant product is 21% solids by weight andhas a degree of substitution of 0.25.

Composite samples of primary sludge were picked up from a municipalsewage treatment plant. Cationic starch at a concentration of 0.5% wasexamined using the following method:

A predetermined amount (based on the dry weight of the sludge) of a0.05% by weight aqueous solution of an anionic polyelectrolyte is addedto 200 ml. of raw primary sludge and mixed back and forth 10 timesbetween two beakers. This anionic polyelectrolyte is a very highmolecular weight synthetic water soluble hydrolyzed polyacrylamidelabeled under the tradename Purifloc A-23 and made by the Dow ChemicalCompany. (In all of the following Examples this anionic polyelectrolytewill simply be referred to as Purifloc A-23).

A specific weight (based on the dry weight of the sludge) of a 0.5% byweight aqueous solution of cationic polyelectrolyte prepared accordingto Example No. 3 is then added, mixed back and forth at 76F. 10; timesbetween two beakers, and transferred to a Buchner funnel fitted withWhatman No. 1 filter paper. The pressure in the filtrate receiver wasreduced to 13 inches Hg and the filtrate collected after 30, 60, andseconds determined. Results are as follows:

I Sludge Amount of Amount of Run (ml.) 70 Solids Anionic Cationic lPolyelectrolyte Oxidized ml. Filtrate 7: Solids Added Starch at(seconds) After Added 30 60 90 120 Filtration 6 Sludge Amount of Amountof Run (ml.) /1 Solids Anionic Cationic Polyelcctrolyte Oxidized ml.Filtratc 7r Solids Added (/z) Starch at (seconds) After Added 192Filtration 4 200 1 1.4 .022 .098 60 97 120 32.6 5 200 .5 .011 .100 70125 170 183 41.2 6 200 9.6 .017 .047 83 123 147 158 45.7 7 200 2.0 .025.100 85 125 172 14.3 x 200 9.5 .025 .092 137 163 55.9 (Average) 9 2005.0 v015 .100 112 158 172 177 43.5 10 200 5.2 .029 .096 150 178 178 44.3(Average) 11 200 9.9 .025 .101 115 130 135 137 31.4 12 200 5.2 .012 .096115 160 172 175 41.6 13 200 5.2 .024 .096 123 168 174 176 43.3 14 2003.6 .024 .097 92 137 158 170 24.0 15 200 9.4 .027 .098 73 100 114 12324.4 16 200 6.0 .025 .100 102 140 153 160 30.0

Notes: Based on dry weight of sludge.

In all tests, the minimal quantities of polyelectrolytes that was usedin Example No. 2. This is due primarily required to increase solids toapproximately 30% in to the small percentage polyelectrolyte (dry basis)by 120 seconds was used as criteria for adequate flocculaweight usedbased on the dry weight of the sludge. In tion and dewatering. The 30%solids level after filtra- 20 all tests, approximately 30% solids after4 minutes vact iS an adequate Solids Content for Sustaining uumfiltration on a filter leaf was used as criteria for adbustion when thefilter cake is later incinerated. equate flocculation and dewatering.

EXAMPLE 3 EXAMPLE NO. 4 A predetermined amount (based on the dry weightof 25 F u l t d t the sludge) of a 0.05% by weight aqueous solution of ils i li gg :1 an anionic polyelectrolyte (Purifloc A-23) is added to Sare e g? 3: X1 t as 2000 ml. of raw primary sludge and mixed. Then aspea i fi Su 5 1 O l :5 e amme cific amount of a 0.5% by weight aqueoussolution of e sewage rea men p a cqmmercla op- 3 eration and the sludgehad an initial SOlldS content of cationic polyelectrolyte (based on thedry weight of the 10.8% by weight. The starch is added to the sewage assludge) prepared according to Example No. 1 15 added a 0.5% by weightsolutlon at a 0.04875% by weight and mixed, being sure not todeflocculate the sludge basis (based on the dry weight of the sewage).with the agitation. A filter leaf with a reduced pressure The amine 0]e1 ctrol te (Purifloc A 23) is added of 13 inches Hg is then loweredinto the conditioned as a 0 057 b i i Solution at a O 0275,? b sludge.Filtrate is collected for 60 seconds and the filter 35 y g que 0 ywerght basis (based on-the dry weight of the sludge). leaf 1S removedand allowed to dry under reduced pres- The treated sludge 1S filtered ona rotary filter at a rate sure for another seconds. The filter cake isthen reof 277.5 wet pounds per minute. The treated sludge has moved andpercent SOlldS and total dry solids are detera SOlldS content of 31.95%.On a dry solids basis, 0.975 mined. Results are as follows.

40 pounds of starch reactant 18 added per ton of dry sludge recovered.This is a very satisfactory performance both Amount of from a cost and atechnical viewpoint.

Cationic Amount of Oxidized Anionic Solids EXAMPLE NO. 5 Sludge StarchPolymer After c Run (mi) S lids Added We) Added Filtration 45 Thefollowing is a 15 day plant size run using oxidized l 2000 65 m5 m2 2&8dent cationic starch in which the starch is 2.2% 0x1- 2 2000 945 932 218dized and has a degree of substitution of 0.25 of an 2 388g 32 -82; gigamine butene halide (particularly l-chloro-4-butenyltrimethylammoniumchloride). The cationic starch is Notes: Based on dry weight of sludge.50 added as a l 1 solution weight. The anionic polyelectrolyte (PuriflocA-23) is added as a 0.05% soluln this Example, the test procedure fordetermining adtion by weight. The sewage treatment plant is a comequateflocculation and dewatering by the polyelecmercial operation and theresults obtained are as foltrolyte has been changed from the Buchnerfunnel test lows:

(untinuctl i Amount of Amount of Solids Dry Pounds Pounds CationicAnionic After Tons Oxidized Anionic Oxidized Polyelectrolyte FiltrationFiltered Cationic Polyelectrolyte Starch Added(%) Starch Added Per RunSolids Added(%)' Per Dry Dry Ton Ton Sludge Sludge (ominucnl Amount ofAmount of 7! Solids Dry Pounds Pounds Cationic Anionic After l'onsOxidized Anionic Oxidized Polyclectrolytc Filtration Filtered CationicPolyelectrolyte Starch Added(%)' Starch Added Per Run 7: Solids AddedU/rPer Dry Dry Tori Ton Sludge Sludge Based on dry weight of the sludge.

In all the daily runs the criteria for adequate flocculation anddewatering was 30% solids level after filtration. The average percentsolids for the entire 15 day run was 32.2%. On a dry solids basis, anaverage of 1.63 pounds cationic starch (0.0815% based on dry weight ofthe sludge) was added per dry ton sludge recovered. This was a verysatisfactory performance both from a cost and technical viewpoint.

What is claimed is:

1. A method of treating raw primary sedimented sewage sludge includingthe steps of adding from 0.016% to O. 1875% by weight (based on the dryweight of the sludge) of gelatinized oxidized cationic starch ether ofamine butene halide to raw primary sedimented sludge, said starch etherhaving a carboxyl content equivalent to a degree of substitution ofabout 0.0036 to about is gelatinized prior to reaction with the aminebutene.

reagent.

3. The method of claim 1 wherein the starch ether is1-chloro-4-butenyltrimethylammonium chloride.

4. The method of claim 1 wherein the starch is dent corn starch.

5. The method of claim 4 wherein the starch is dent corn starch and theamine butene halide is l-chloro-4- butenyltrimethylammonium chloride.

1. A METHOD OF TREATING RAW PRIMARY SEDIMENTED SEWAGE SLUDGE INCLUDINGTHE STEPS OF ADDING FROM 0.016% TO 0.1875% BY WEIGHT (BASED ON THE DRYWEIGHT OF THE SLUDGE) OF GELATINIZED OXIDIZED CATIONIC STARCH ETHER OFAMINE BUTENE HALIDE TO RAW PRIMARY SEDIMENTED SLUDGE, SAID STARCH ETHERHAVING A CARBOXYL CONTENT EQUIVALENT TO A DEGREE OF SUBSTITUTION OFABOUT 0.0036 TO ABOUT 0.0108 AND A DEGREE SUBSTITUTION OF AMINE BUTENEHALIDE OF ABOUT 0.15 TO 0.25, FLOCCULATING THE SLUDGE, AND DEWATERINGTHE SLUDGE TO BELOW ABOUT 70% MOISTURE.
 2. The method of claim 1 whereinthe oxidized starch is gelatinized prior to reaction with the aminebutene reagent.
 3. The method of claim 1 wherein the starch ether is1-chloro-4-butenyltrimethylammonium chloride.
 4. The method of claim 1wherein the starch is dent corn starch.
 5. The method of claim 4 whereinthe starch is dent corn starch and the amine butene halide is1-chloro-4-butenyltrimethylammonium chloride.